GEA Grasso - Page 53

Grasso
Refri
g
eration Division
GRASSO SYSTEM CONTROL
01.2004/1 638660E_chapter2.doc Chap. 2 - 17
2.7.2.6 Low and high suction pressure alarm
Both low and high suction pressures are monitored. In case the suction pressure becomes too low or too high an
alarm is generated. Both alarms do not become active until the start up process has been completed. After
starting the compressor motor an additional delay time of 5 minutes becomes active for the high suction
pressure alarm only. During this time the suction pressure is allowed to exceed its maximum limit.
The low suction pressure alarm function is illustrated in the following diagram.
P
suc
Suction pressure
A.. Time characteristic of the suction
pressure
V.. Forced reduction of the capacity
due too low suction pressure
B.. Low suction pressure limitation
active
T.. Limit timer active; After that this
timer has expired the capacity
control is enabled again and the
compressor capacity can be
increased.
b.. Limit value for disabling capacity
increase
f.. Limit value for forced reduction of
capacity
W.. Warning limit
Al.. Alarm limit
ML W.. Warning active
ML A.. Alarm active
3.. Reset of the active alarm
Figure 2.21, Low suction pressure alarm
Suction press 
Psuc low alarm 
Low warning + 
Suction pressure: Actual suction pressure in bar (a)
Psuc low alarm: Alarm limit for minimum suction pressure in bar (a)
Warning: Enter the warning value as an offset to the alarm limit in
Limit values 01 >> bar